Among the following examples, the species that behave(s) as a Lewis acid is/are: 
\(\mathrm{BF}_3, \mathrm{SnCl}_2, \mathrm{SnCl}_4\)

1. Stannous chloride, Stannic chloride
2. $B{F}_3$, Stannous chloride
3. Only $B{F}_3$
4. $B{F}_3$, Stannous chloride, Stannic chloride

The correct relation between dissociation constants of a di-basic acid is:

1. $K{a}_1=K{a}_2$

2. $K{a}_1>K{a}_2$

3. $K{a}_1<K{a}_2$

4. $K{a}_1=\frac{1}{K{a}_2}$

Conjugate acid of NH₂^– is:

1. NH₄OH

2. NH₄⁺

3. \(NH_{2}^{-}\)

4. NH₃

A compound, among the following, that cannot be classified as a protonic acid is: